There are a variety of applications in which apparatus, such as electronic gear, is provided with a covering to protect it from the surrounding ambient but is provided with a vent opening so that the air can circulate in either direction through the vent opening, for example to avoid variations in air pressure within the covering due to temperature changes. One example is electronic gear positioned at a measurement and/or control point in an industrial process-control system; other analogous situations will occur to one skilled in the art.
In some instances the vent opening is subject to impingement by a moving liquid, for example a rapidly moving stream of water from a cleansing hose, or wind-blown rain, as examples. Such liquid can easily enter the vent opening and undesirably contact the apparatus inside the covering, if protection is not provided.
A large variety of vent systems are known which can be placed in or over such a vent opening in an effort to prevent entry of surrounding liquid, typically water, while permitting the flow through the vent opening of a gas, typically air. However, such known systems have been limited with respect to effectiveness, size, cost, longevity and/or freedom from maintenance requirements, as well as being effective in only one or possibly two positions.
As an example, a standard of the National Electrical Manufacturers Association known as NEMA STANDARD NO. 250-1991 requires testing of a vent system by impinging the vent system with a stream of water flowing at 67 gallons per minute from a 1" diameter nozzle located 10' away from the vent system. To pass this NEMA test, the vent system must provide for easy air flow through the vent opening while preventing the water from the nozzle from entering the vent opening, no matter from which direction it is applied. These requirements have been found difficult to provide.
The preferred embodiment of the present invention meets these NEMA requirements, and is also conveniently small and sturdy, and has a long trouble-free life, as desired.